Drawing Die Provided With Slant Blank Clamping Surface

ABSTRACT

A drawing die provided with a slant blank clamping surface, where the drawing die includes a lower die base, a lower die secured on the lower die base, an upper die base, a punch fixing plate secured on the upper die base, a punch secured on the punch fixing plate, where the punch is capable of moving relative to the lower die, and a blank holder capable of moving relative to and in parallel with the punch fixing plate, where a blank pressing surface facing the lower die of the blank holder is provided with a slant surface and/or a lower die surface facing the blank holder of the lower die is provided with a slant surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of Taiwan Patent Application No. 103120827, filed on Jun. 17, 2014, which is hereby incorporated by reference for all purposes as if fully set forth herein.

BACKGROUND

1. Technical Field

The present invention relates to a drawing die, and in particular, to a drawing die provided with a surface that is slant relative to a blank clamping surface for clamping and drawing a blank.

2. Related Art

Drawing forming is stamping a flat sheet metal (for example, a blank) by using a drawing die to form a required product shape. Please refer to FIG. 1A to FIG. 1D, which are structural flowcharts of processing a blank by using a drawing die in the prior art. FIG. 1E is a schematic view of stresses on parts of a finished product 20 formed by a blank 19. FIG. 1A shows a drawing die 10 in the prior art, including a lower die base 11, a lower die 12, an ejection apparatus 13, a positioning plate 14, a blank holder 15, an upper die base 16, a punch 17, a punch fixing plate 18 and a blank 19. The lower die 12, which is secured on the lower die base 11, coordinates with the blank-holder 15 to clamp the blank 19, and coordinates with the corresponding punch 17 to perform drawing processing on the blank 19. FIG. 1B shows a process in which the blank holder 15 descends following a stroke and collides with the blank 19 in a working process of the drawing die 10. FIG. 1C shows a process in which the punch 17 presses the blank 19 to form a shape in a drawing process. FIG. 1D shows a situation where the finished product 20 is ejected by the ejection apparatus 13 after the processing is completed. FIG. 1E is a schematic view of stresses on parts of the finished product 20 in a drawing process in which the blank 19 forms the finished product 20.

Please refer to FIG. 1C, FIG. 1D, and FIG. 1E again. In the foregoing drawing die 10, when the blank 19 of a sheet metal forms the finished product 20 in a cup shape or a barrel shape (the cup shape is used herein as an example), a drawing force Fa applied by the punch 17 on the blank 19 must overcome a strain force f1 required for the strain of the blank, a friction force f2 between the blank holder 15 and the blank 19, and a friction force f3 between the blank 19 and the lower die 12. Besides, when the punch 17 descends to perform forming and the blank 19 gradually forms the finished product 20, an outer edge surface 201 of the finished product 20 gradually shrinks; at the same time, the thickness of a top 202 of the finished product 20 gradually increases, and a shoulder 203 is subject to a bending moment and bends. When a blank pressing force Fb applied by the blank holder 15 on the top 202 of the finished product 20 is not sufficient to resist a circumferential compression stress on the top 202, the top 202 wrinkles Besides, the blank pressing force Fb affects the magnitude of the friction force between the blank holder 15 and the blank 19 and the magnitude of the friction force between the blank 19 and the lower die 12.

In another aspect, during the forming, a side wall 204 of the finished product 20 is subject to a drawing force of the punch 17; therefore, the thickness of the side wall 204 of the finished product 20 gradually decreases. When the stress of the side wall 204 exceeds the strength of a material of the side wall 204, an area, close to a bottom 205, of the side wall 204 cracks.

SUMMARY

An objective of the present invention is to provide a drawing die provided with a slant blank clamping surface for clamping and processing a blank.

To achieve the foregoing objective, a technical means of a drawing die provided with a slant blank clamping surface of the present invention comprises that: the drawing die comprises a lower die base, a lower die secured on the lower die base, an upper die base, a punch fixing plate secured on the upper die base, a punch secured on the punch fixing plate, where the punch is capable of moving relative to the lower die, and a blank holder capable of moving relative to and in parallel with the punch fixing plate, where the blank pressing surface facing the lower die of the blank pressing plate is provided with a slant surface.

In an embodiment, the slant surface slants towards a center shaft of the drawing die.

In an embodiment, a shape of a cross section of the slant surface comprises an irregular shape, or comprises a geometrical shape of a slant line, a slant line plus a horizontal line, a curved line, or a curved line plus a horizontal line.

To achieve the foregoing objective, the present invention provides another technical means of a drawing die provided with a slant blank clamping surface, which comprises that: the drawing die comprises a lower die base, a lower die secured on the lower die base, an upper die base, a punch fixing plate secured on the upper die holder, a punch secured on the punch fixing plate, where the punch is capable of moving relative to the lower die, and a blank holder capable of moving relative to and in parallel with the punch fixing plate, where the blank supporting surface facing the blank holder of the lower die is provided with a slant surface.

In an embodiment, the slant surface slants towards a center shaft of the drawing die.

In an embodiment, a shape of a cross section of the slant surface comprises an irregular shape, or comprises a geometrical shape of a slant line, a slant line plus a horizontal line, a curved line, or a curved line plus a horizontal line.

The present invention has the following features: different from a conventional structure of a blank holder, in the present invention, a slant surface is disposed on a surface facing a plate blank of a blank holder, and/or a slant surface is disposed on a surface supporting a plate blank of a lower die; compared with a case in which no slant surface is disposed on a blank holder/lower die, when a drawing die applies a same downward blank pressing force, disposing the slant surface can increase a thrust force in a direction from the plate blank to a center shaft of the die and decrease a friction force between the blank holder and the plate blank and/or a friction force between the lower die and the plate blank, thereby reducing a probability that the thickness of the plate blank decreases and improving formability of the drawing die.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will become more fully understood from the detailed description given herein below for illustration only, and thus are not limitative of the disclosure, and wherein:

FIG. 1A to FIG. 1D are structural flowcharts of processing a blank by using a drawing die in the prior art;

FIG. 1E is a schematic view of stresses on parts of a finished product in a process in which a blank forms the finished product;

FIG. 2 is a schematic view of a structure profile of a drawing die provided with a slant blank clamping surface before drawing is performed according to an embodiment of the present invention;

FIG. 3 is an enlarged view of a part of which a serial number is 3 in FIG. 2;

FIG. 4 is an enlarged view of a part of which a serial number is 4 in FIG. 2;

FIG. 5 is a schematic view of a structure profile of a drawing die provided with a slant blank clamping surface when drawing is performed according to an embodiment of the present invention;

FIG. 6 is an enlarged view of a part of which a serial number is 6 in FIG. 5;

FIG. 7 is a schematic view of a force applied by a slant surface of a blank holder on a board in FIG. 6 decomposed into a thrust force as a component force;

FIG. 8 is an enlarged view of a part of which a serial number is 8 in FIG. 5; and

FIG. 9 is a schematic view of a force applied by a slant surface of a lower die on a board in FIG. 8 decomposed into a thrust force as a component force.

DETAILED DESCRIPTION

Embodiments of the present invention are described as follows with reference to the accompanying drawings.

Please refer to FIG. 2 to FIG. 9 first. A drawing die 30 in this embodiment includes: a lower die base 31, an upper die base 32, a lower die 311 secured on the lower die base 31, where the lower die 311 includes a die cavity 3112, and a positioning plate 33 used for positioning a to-be-processed blank W made of a sheet metal is disposed on the lower die 311, and a punch 3211 secured on a punch fixing plate 321 on a bottom of the upper die base 32, where a blank holder 3212 capable of moving with the punch fixing plate 321 is disposed between the punch 3211 and the lower die 311. The lower die 311 can coordinate with the punch 3211 moving relative to the lower die 311, so as to perform drawing processing on the blank W. A blank pressing surface 32121 facing the lower die 311 of the blank holder 3212 is a slant surface, for example, the slant surface may have a slant angle A, but the present invention is not limited thereto (for example, the slant surface has multiple slant angles or is curved); or a blank supporting surface 3111 facing the blank holder 3212 of the lower die 311 is a slant surface, for example, the slant surface may have a slant angle A′, but the present invention is not limited thereto (for example, the slant surface has multiple slant angles or is curved). Certainly, in an embodiment, the foregoing examples may also be combined, that is, both the blank pressing surface 32121 and the blank supporting surface 3111 are slant surfaces.

Further, as shown in FIG. 2, FIG. 3, and FIG. 4, in an embodiment, the slant surface slants towards a center shaft C of the die cavity 3112 of the drawing die 30 (a central line in FIG. 3 or FIG. 4 represents a reference surface in a no slant state).

A schematic view of a clamping relationship between the foregoing slant angle A on the blank pressing surface 32121 of the blank holder 3212 or the foregoing slant angle A′ on the blank supporting surface 3111 of the lower die 311 and the blank W is as shown in FIG. 5. Besides, FIG. 6 and FIG. 8 are enlarged schematic views of parts in FIG. 5.

Please continue to refer to FIG. 5, FIG. 6, and FIG. 7. In an embodiment in FIG. 6, after the blank holder 3212 applies a blank pressing force Fb′ to clamp the blank W, when the punch 3211 presses the blank W downward with a drawing force Fa′ to draw the blank W, the slant surface of the blank pressing surface 32121 applies a force AF1 on a top surface of the blank W, where the force AF1 may be decomposed into a horizontal thrust force B1 and a vertical downward pressing force (shown in FIG. 7), and a thrusting direction of the thrust force B1 is towards the center shaft C of the die.

Please refer to FIG. 5, FIG. 8, and FIG. 9 then. In an embodiment in FIG. 8, after the blank holder 3212 applies a blank pressing force Fb′ to clamp the blank W, when the punch 3211 presses the blank W downward with a drawing force Fa′ to draw the blank W, the slant surface of the blank supporting surface 3111 applies a force AF2 on a bottom surface of the blank W, where the force AF2 may be decomposed into a horizontal thrust force B2 and a vertical upward jacking force (shown in FIG. 9), and a thrusting direction of the thrust force B2 is towards the center shaft C of the die.

In an embodiment, a shape of a cross section of the slant surface disposed on the blank pressing surface and/or the blank supporting surface includes an irregular shape, or includes a geometrical shape of a slant line, a slant line plus a horizontal line, a curved line, or a curved line plus a horizontal line.

It is worth mentioning that the foregoing slant angle of the slant surface of the slant blank pressing surface (disposed on a bottom surface of the blank holder) and/or the slant blank supporting surface (disposed on a top surface of the lower die) in the present invention is a slant angle which is within a tolerance range required for not affecting a finished product processed by using the drawing die.

Compared with the prior art, the present invention has the following advantages: a slant surface is disposed on a surface facing a plate blank of a blank holder, and/or a slant surface is disposed on a surface supporting a plate blank of a lower die; compared with a case in which no slant surface is disposed on a blank holder/lower die, when a drawing die applies a same downward blank pressing force, disposing the slant surface can increase a thrust force in a direction from the plate blank to a center shaft of the die and decrease a friction force between the blank holder and the plate blank and/or a friction force between the lower die and the plate blank, thereby reducing a probability that the thickness of the plate blank decreases and improving formability of the drawing die.

In conclusion, the foregoing is merely preferred implementation manners or embodiments presenting the technical means adopted in the present invention to solve the problem, and is not intended to limit the implementation scope of the patent of the present invention. That is, all equivalent variations and modifications in accordance with the idea in the application scope of the patent of the present invention or made according to the scope of the patent of the present invention are covered by the scope of the patent of the present invention. 

What is claimed is:
 1. A drawing die provided with a slant blank clamping surface, wherein the drawing die comprises a lower die base, a lower die secured on the lower die base, wherein the lower die is provided with a die cavity, an upper die base, a punch fixing plate secured on the upper die base, a punch secured on the punch fixing plate, wherein the punch is capable of moving relative to the lower die, and a blank holder disposed between the punch and the lower die and capable of moving relative to and in parallel with the punch fixing plate, wherein a blank pressing surface facing the lower die of the blank holder is provided with a slant surface.
 2. The drawing die provided with a slant blank clamping surface according to claim 1, wherein the slant surface slants towards a center shaft of the die cavity of the drawing die.
 3. The drawing die provided with a slant blank clamping surface according to claim 1, wherein a shape of a cross section of the slant surface comprises an irregular shape.
 4. The drawing die provided with a slant blank clamping surface according to claim 1, wherein a shape of a cross section of the slant surface comprises a geometrical shape of a slant line, a slant line plus a horizontal line, a curved line, or a curved line plus a horizontal line.
 5. A drawing die provided with a slant blank clamping surface, wherein the drawing die comprises a lower die base, a lower die secured on the lower die base, wherein the lower die is provided with a die cavity, an upper die base, an upper punch fixing plate secured on the upper die base, a punch secured on the punch fixing plate, wherein the punch is capable of moving relative to the lower die, and a blank holder disposed between the punch and the lower die and capable of moving relative to and in parallel with the punch fixing plate, wherein a blank supporting surface facing the blank holder of the lower die is provided with a slant surface.
 6. The drawing die provided with a slant blank clamping surface according to claim 5, wherein the slant surface slants towards a center shaft of the drawing die.
 7. The drawing die provided with a slant blank clamping surface according to claim 5, wherein a shape of a cross section of the slant surface comprises an irregular shape.
 8. The drawing die provided with a slant blank clamping surface according to claim 5, wherein a shape of a cross section of the slant surface comprises a geometrical shape of a slant line, a slant line plus a horizontal line, a curved line, or a curved line plus a horizontal line. 